GridGetSelection retrieves the current selection.
rmSelection is matrix with four columns.
Each matrix row contains one selection range:
Col1: First selected column, Col2: First selected row, Col3: Last selected column, Col4: Last selected row.
Column and row numbering starts with 1.
If one of the values is 0 the entire row or column is selected.
All functions starting with Grid access the data browser. If the browser dialog isn’t open, these functions return an invalid value.